The present invention generally relates to methods and systems for identifying reliability risk die on a wafer, and more specifically relates to a method and system for selectively identifying reliability risk die based on characteristics of local regions on the wafer.
Presently, in identifying reliability risk die on a wafer, it is typically assumed that failing die are primarily caused by particle type defects, that particle type defects occur in localized regions on the wafer, and that test coverage is never 100 percent, so die with actual defects will still pass wafer sort tests. Hence, good die in bad regions are likely to be reliability risks.
A prior art approach at identifying reliability risk die on the wafer is illustrated in FIG. 1. A threshold is pre-set with regard to yield in the local region around the die. If the yield is less than the pre-set threshold, the die is downgraded. On the other hand, if the yield is not less than the pre-set threshold, the die is not downgraded. The problem with the approach is that, contrary to the first assumption identified above, not all failing die are due to particle type defects. Hence, the approach illustrated in FIG. 1 typically results in excessive downgrading.